|Year : 2021 | Volume
| Issue : 4 | Page : 46-49
“Crossed C1 Lateral Mass–C2 Subfacetal Screw and Rod Construct” for Atlantoaxial Fixation in Patients with High-Riding Vertebral Artery: A Technical Note
Vinu V Gopal1, Geo Paul Kurikkattayil Jose2, Paruvakkattil Kunjan Balakrishnan3
1 Associate Professor, Department of Neurosurgery, Government Medical College Kottayam, Kerala, India
2 Senior Resident, Department of Neurosurgery, Government Medical College Kottayam, Kerala, India
3 Professor, Department of Neurosurgery, Government Medical College Kottayam, Kerala, India
|Date of Submission||03-Oct-2021|
|Date of Acceptance||10-Oct-2021|
|Date of Web Publication||24-Dec-2021|
Geo Paul Kurikkattayil Jose
Senior Resident, Department of Neurosurgery, Government Medical College Kottayam, Kerala
Source of Support: None, Conflict of Interest: None
Background: Goel–Laheri's posterior C1/C2 fixation technique is the gold standard procedure for atlantoaxial dislocation (AAD) and basilar invagination. Coexisitng vertebral artery anomalies such as high-riding vertebral arteries pose an increased risk of vertebral artery injury during instrumentation. Alternate technique for avoiding vertebral artery injury in such cases like translaminar screw fixation had been associated with a high chance for screw pull out, resulting in an unstable construct. This case report introduces a novel, cost-effective technique of atlantoaxial fixation with a “bilateral crossed C1 lateral mass-C2 subfacetal screw and rod construct” in patients with atlantoaxial subluxation with high-riding vertebral arteries.
Case Presentation: A 63-year-old male presented with complaints of neck pain and difficulty in walking. On physical examination, he had features of high cervical myelopathy. Imaging revealed AAD with bilateral high-riding vertebral arteries. He was treated with “Crossed C1 lateral mass-C2 subfacetal screw and rod fixation” without evidence of vertebral artery injury or neurological deficits. Postoperatively, the patient showed significant improvement in pain and Nurick score.
Conclusions: This technique has the uniqueness of providing a stable, rigid fixation of the atlantoaxial joint with screws inserted into the C2 body providing good bone purchase and at the same time avoid vertebral artery injury in high riding cases. The surgical technique is demonstrated in a detailed manner in this technical note.
Keywords: Atlantoaxial dislocation, C2 subfacetal screw, high riding, vertebral artery
|How to cite this article:|
Gopal VV, Kurikkattayil Jose GP, Balakrishnan PK. “Crossed C1 Lateral Mass–C2 Subfacetal Screw and Rod Construct” for Atlantoaxial Fixation in Patients with High-Riding Vertebral Artery: A Technical Note. J Spinal Surg 2021;8:46-9
|How to cite this URL:|
Gopal VV, Kurikkattayil Jose GP, Balakrishnan PK. “Crossed C1 Lateral Mass–C2 Subfacetal Screw and Rod Construct” for Atlantoaxial Fixation in Patients with High-Riding Vertebral Artery: A Technical Note. J Spinal Surg [serial online] 2021 [cited 2022 Jan 21];8:46-9. Available from: http://www.jossworld.org/text.asp?2021/8/4/46/333625
| Introduction|| |
Goel–Laheri's posterior C1/C2 fixation technique using C1 lateral mass screw and C2 pedicle screw is the gold standard procedure for atlantoaxial dislocation (AAD) and basilar invagination (BI). However, in the case of high-riding vertebral arteries, the chance of vertebral artery injury is around 49% with C2 pedicle screw fixation. Alternate techniques for avoiding vertebral artery injury such as translaminar screw fixation have been described. However, these techniques have a high chance of screw pull out, providing an unstable construct. We have described a novel, cost-effective technique of “bilateral crossed C1 lateral mass-C2 subfacetal screw and rod construct” for C1/C2 posterior fusion, avoiding vertebral artery injury. This technique also provides stable, rigid fixation of the atlantoaxial joint with screws inserted into the C2 body providing a good bone purchase.
| Case Presentation|| |
A 63-year-old male presented with neck pain and difficulty in walking having features suggestive of high cervical myelopathy such as brisk deep tendon reflex and extensor plantar. There was no motor weakness or sensory impairment found on detailed neurological assessment (Nurick grade 2).
The patient was evaluated with computed tomography (CT) and magnetic resonance imaging of the craniovertebral junction, diagnosed with irreducible AAD and BI. The CT angiography revealed bilateral high-riding vertebral arteries [Figure 1]. The conventional C1 lateral mass–C2 pedicle screw and rod fixation technique was not planned due to associated bilateral high-riding vertebral arteries with the high risk of injury. After obtaining informed written consent, we planned “bilateral crossed C1 lateral mass-C2 subfacetal screw and rod construct” for posterior C1/C2 fusion.
|Figure 1: (a) Showing high-riding vertebral artery in which isthmus height (red arrow-yellow line) is 5 mm and internal height (green arrow-red line) is 2 mm on a sagittal image. (b) Showing narrow pedicle with pedicle width (yellow arrow-green line) of 4 mm|
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Planning the trajectory and length of the screw
After obtaining informed written consent in regional language, the pros and cons of surgery were explained to the patient and his relatives. As a part of preoperative evaluation for C2 subfacetal screw insertion, the trajectory of the screw, screw length, and density of bone stock of C2 facet were assessed and planned using 3D CT virtual reality images [Figure 2].
|Figure 2: (a) Reflecting planning using three-dimensional computed tomography virtual reality images and, (b) denotes screw trajectory and bone stock length (yellow arrows)|
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The patient was positioned in the prone position with slight neck flexion using the skull clamp. Midline skin incision from inion to C4 spinous process was adopted. After routine midline exposure, both C1 and C2 joints were exposed till the complete exposure of lateral border of facet joints.
Entry point and trajectory
The entry point of C1 lateral mass screws was just lateral to the midpoint of the posterior surface of C1 lateral mass in the direction of 10°–15° medially and 10°–15° cranially. C2 subfacetal screw was inserted 1 mm medial and 2 mm caudal to the midpoint of superior facet, directed 15°–20° medially and 30° inferiorly into the C2 body [Figure 3]. The technique requires only single C-arm exposure to confirm the screw position [Figure 4]. For the screw insertion, the trajectory was initially made using a 2 mm diamond drill bit followed by tapping with a 3.5 mm tap. For C1 lateral mass, we used 3.5 mm (width) ×36 mm (length) screws, and for the C2 facet, 3.5 mm (width) ×24 mm (length) screws [Figure 5].
|Figure 3: Entry point for C1 lateral mass screw (blue dot) and C2 subfacetal screw entry point as red dot|
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|Figure 4: Shows intraoperative X-ray lateral view of the neck reflecting C1 lateral mass and C2 subfacetal screw trajectory|
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|Figure 5: Intraoperative picture of crossed screws after fixation- (a) after C2 screw insertion showing entry point; (b) Showing crossed screws after both C2 and C1 screw insertion; (c) after bilateral rod fixation|
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Crossing of screws and C1/C2 distraction with spacer
More medial insertion points of the C2 screw and more lateral insertion points of the C1 screw help screws in the crossing, particularly preventing the screw heads from interfering and providing a good construct and ergonomics for the safe fixation. In some cases, drilling and tapping the C2 screw after C1 screw insertion is challenging, and in such cases, we drill and tap the trajectory of both C1 and C2 screws first before the screw insertion. Compared to the conventional technique, long screws were used (for better purchase and to facilitate the rod fixation in the closed space). It also helps in distraction and compression of the atlantoaxial joint without much traction on vertebral arteries. Use of the longer screws helps in the better bone purchase and easy alignment of screw heads for rod fixation. Autograft-like bone chips studded titanium spacer was applied to reduce the dislocation, and distraction followed by compression of the atlantoaxial joint was done to facilitate the fusion.
The postoperative period was uneventful, with no neurological deficits. Postoperative CT showed satisfactory screw positions [Figure 6]. He was discharged home on 3rd postoperative day.
|Figure 6: (a) Computed tomography CVJ sagittal image with the C1 C2 screws; (b) three-dimensional reconstructed image of crossed C1–C2 screw; (c) three-dimensional computed tomography reconstructed image showing C2 subfacetal screw; and (d) computed tomography three-dimensional reconstructed image of C1 lateral mass screws|
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On follow-up after 6 weeks, the wound had healed completely, neck pain reduced, and postoperative Nurick score improved from Grade 2 to Grade 1.
| Discussion|| |
Pathologies involving craniovertebral junction such as AAD and BI are usually treated by various posterior screw fixation techniques, including C1 lateral mass–C2 pedicle screw fixation by Goel and Laheri, transarticular screw fixation by Magerl, and C2 laminar screw fixation by Wright.,, C1 lateral mass–C2 pedicle screw fixation is considered the gold standard for atlantoaxial fixation. The C2 pedicle screw insertion techniques such as transpedicular/transarticular C2 screw fixations in case of high-riding vertebral artery are very challenging due to narrow pedicle., Vertebral artery injury poses serious consequences, including uncontrollable bleeding, cerebral ischemia, pseudo-aneurysm, and death., In the study by Yeom et al. among 269 patients (538 potential screw insertions), there were 78 high-riding vertebral arteries, vertebral artery groove violation by C2 pedicle screw fixation was seen in 49% with the conventional Goel and Laheri technique. In contrast, with transarticular screw fixation, it was 63%. Although the C2 translaminar screw is a good alternative, the screw pullout rate was very high due to poor bone stock.
Concept of C2 subfacetal screw
According to Menon and Raniga, there is a dense, compact bone below the C2 facet. The concept of C2 subfacetal screws is based on this fact. The advantage of the C2 subfacetal screw technique is that it helps to place C2 screws without fear of vertebral artery injury in high riding cases. A similar method was described by Patkar, the C2 screw insertion point is few millimeters below the midpoint of the superior facet joint. Case series by Salunke et al. subfacetal screw was inserted directly into C2 body starting from the medial part of subfacetal region, 15°–20° cranially and 30°–40°- medially. Comparatively, our technique of bilateral crossed C1 lateral mass–C2 subfacetal screw and rod construct is unique; we used polyaxial screw and rod construct, particularly in a crossed fashion, to help in distraction and compression of the atlantoaxial joint. This method does facilitate not only bony fusion but also avoids undue traction on the vertebral artery. Here, the technical modification of more medial insertion point of C2 screw and more lateral insertion point of C1 screw helps screw fixation in crossing, providing a good screw ergonomics. The use of longer screws helps in the better bone purchase, easy alignment of screw heads for rod fixation, and also it helps in distraction–compression maneuver if required. As it does not need any costly implants, it is also cost-effective.
| Conclusions|| |
This novel, cost-effective technique of “Crossed C1 lateral mass-C2 subfacetal screw and rod construct” for atlantoaxial fixation provides a good alternative for avoiding vertebral artery injury in high-riding vertebral artery cases. The results may be further validated following a multicenter randomized controlled trial following a pilot study.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]